Centering sensor and controller

ABSTRACT

A system for sensing and controlling the centering of a sheet continuously fed through a machine includes a pair of laterally spaced apart sensing arms spring biased into contact with the opposite edges of the sheet as the sheet is being fed through the machine. Separate transducers responsive to movement of the sensing arms produce electrical signals representing the actual position of each edge of the sheet. The signals from both transducers are compared with input signals representing the known centered position of the sheet to provide an error signal for continuously indicating the magnitude and direction of the deviation from center independently of variations in the width of the sheet or any desired lateral shifting of the sheet as it travels through the machine. A controller responsive to the error signal produces control signals for driving a servo motor which moves the sheet laterally to keep it on center.

[4 1 Sept. 30, 1975 l CENTERING SENSOR AND CONTROLLER Gary D. McCann, 2455 E. Chevy Chase Dr Glendale. Calif. 91206 22 Filed: Mar. 14, 1974 211 Appl. No: 451,221

Related US. Application Data [63] Continuation-in-part of Ser. No. 343.01 1. March 21.

1973, Pat. NO. 3 806,0l3.

[76] Inventor:

[57] ABSTRACT A system for sensing and controlling the centering of a sheet continuously fed through a machine includes a pair of laterally spaced apart sensing arms spring biased into contact with the opposite edges of the sheet as the sheet is being fed through the machine. Separate transducers responsive to movement of the sensing arms produce electrical signals representing the actual position of each edge of the sheet. The signals from both transducers are compared with input signals representing the known centered position of the sheet E g 18 to provide an error signal for continuously indicating [56] References Cited travels through the machinev A controller responsive UNITED STATES PATENTS to the error signal produces control signals for driving 7 1075.1 1 l 3/1937 Gulliksen 226/23 a servo motor which moves the sheet laterally to keep 3,322.96} 5/1967 Pages 242/57.l X i on Centcr 3.490 674 [H970 Ott 226/19 Primary E.\'umincrRichard A. Schacher Attorney, Agent. or Firm-Christie, Parker & Hale the magnitude and direction of the deviation from center independently of variations in the width of the sheet or any desired lateral shifting of the sheet as it US. Patent Sept. 30,1975 Shcet I 01*4 3,908,881

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US. Patent Sept. 30,1975 Sheet 2 of4 3,908,881

.pI UQ U.S. Patent Sept. 30,1975 Sheet 3 of4 3,908,881

CENTERING SENSOR AND CONTROLLER CROSS-REFERENCE TO RELATED APPLICATION This is a continuation-in-part of application Ser. No. 343,011, filed Mar. 21, 1973, now US. Pat. No.

BACKGROUND OF THE INVENTION This invention relates to a system for sensing the centering of work continuously fed through a machine,'and for controlling the deviation of the work from a known centered position independently of the width of the work or its lateral movement through the machine.

There are industrial applications in which work is continuously fed through a machine in acentered position. For example, in the carpet industry a mat of woven jute is continuously unrolled and fed through a tufting machine. The jute provides the primary backing for a carpet, and the tufting machine includes reciprocating needles which automatically thread strands of yarn into the jute to produce appropriately designed tufting for the carpet.

Typically, the tufting covers a major portion of the jute backing sheet. A selvedge (section which has no tufting) several inches in width is left along each marginal edge of the jute. The selvedge strips are then engaged with pins carried on a chain conveyor to feed the tufted jute backing sheet through an oven in which latex and a second backing sheet areapplied to .the jute. The two selvedge strips are then trimmed to provide the finished carpet. The selvedge strips usually are trimmed by feeding the carpet pasta pair of fixedknife blades spaced apart by a distance equal to the width of the finished carpet. I

It is of critical importance to maintain the jute backing sheet in a continuous on-center position when tufting is applied to it. If the tufting deviates from a centered position on the jute, a blank untufted area will be present at the edge of the finished carpet after the selvedge strips are trimmed. A carpet roll having such un tufted areas is considered in the industry to be a factory second, and generally can be sold only at such a substantial discount that money will be lost by the carpet manufacturer. i

The manufacturer can insure against blank areas being present at the edges of the finished carpet by adding several inches of excess tufting. However, even a few extra needles added to the tufting operation can cost the manufacturer an extra several hundred dollars per day per machine. If the carpet can be kept reasonably on-center during tufting operations, less excess yarn is needed, which can provide the manufacturer a substantial cost savings.

Generally, the operator of the tufting machine visually monitors the centering of the jute backing sheet. This task is difficult, though, because the two edges of the jute are spaced a relatively long distance apart (about 150 inches). In one prior art method of mechanically monitoring the centering of the jute, a microswitch located along one edge of the jute activates an alarm whenever the width of the selvedge strip-exceeds a predetermined amount. However, this method has not proved to be practical, because the width of the jute backing sheet usually varies several inches between one place and another in a givenroll; and this variation in width will cause errors in thelcetering of the tufting. Moreover, many carpets are made by'constantly shifting thejute back and forth laterally to apply the tufting in a zigzag pattern. This lateral shifting of the jute complicates the process of determining, either mechanically or visually, when the tufting is off-center.

SUMMARY OF THE INVENTION Briefly, this invention provides a system for sensing and controlling the centering of work continuously fed through a machine in which the work has a known centered position; The system includes means for sensing the instantaneous position of each edge of the workas it moves through the machine. The sensing means produces a first output representing the position of one edge, and a second output representingthe position of the other edge. The first and second outputs are combined to produce an error signal representing'the instantaneous lateral deviation of the work 'from its'centered position. The error signal is then fed to a controller'for moving the work laterally to keep it on the. desired centered position.

In a preferred form of the invention, the sensing means comprise a pair of sensing ar 'ms continuously en= 'gaged with the opposite longitudinal edges of the work independently of variations in the width of the work or lateral shifting-of the work as it travels through the machine. Thus, the sensingsystem is especially suitable for use in the carpet industry, because the movement of the sensing arms can provide indications of the instantaneous position of each edge of a jute backing sheet independently of the usual variations in its width or lateral reciprocating motion of thejute when tufting is applied to it in a Zigzag patternrTransducers controlled by movement of the sensing arms'p'roduce output signals which are compared with input signals representing the instantaneous known centered position of the jute to provide the error signal for indicating themagnitude and direction of the deviation from center. The

error signal can be fed to the controller to. move the jutelaterally toward its on-center positionfwhenthe jute deviates from its .true centered position by a selected amount.

. 1 These and other aspects of the invention will be more fully understood by referring to thefollowing detailed description and the accompanying drawings.

BRIEFFIDESCRIPTION OF THE DRAWINGS FIG. 1 is a fragmentary perspective view showing the centering sensing and control system ofzthis invention used in combination with a carpet tufting machine;

FIG. 2 is an enlarged fragmentary elevation view showing an edge positionsensing device used in the'sys tem of FIG. 1;

FIG. 3 is an electrical schematic diagramof the centering sensing and control system of this invention;

FIG. 4 is a schematic elevation view showing a meter for indicating the instantaneous deviation of the. carpet shown in FIG. 1 from a known centered position in the carpet tufting machine;

FIG. 5 is anelectrical schematic diagram of a controllerl'for moving the carpet toward its on-center position in response to error signals from the edge position sensors; and

'FI G. 6- is a fragmentary schematic perspective view illustrating aprefer'red means for mechanically moving the carpet backing in response to correction'signals from the' controller.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIG. 1, the present invention will be described in the context of its use in a carpet tufting machine 10, although it will be recognized that the inven tion can be used in other machines through which work is continuously fed in a known centered position. A sheet 12 ofjute is continuously unrolled from a storage roll 13 and fed in a longitudinal direction through the tufting machine. Thejute is fed under a vertically reciprocating needle bar 14. Separate strands 16 of yarn are threaded through respective vertically disposed needles 18 carried by needle bar 14. Push rods 20 connected to needle bar 14 are driven up and down by a drive mechanism (not shown) to reciprocate the needle bar and stitch yarn 16 into the travelingjute backing sheet 12 to provide tufting for the jute.

The tufting is commonly stitched in a zigzag pattern as shown at 22. The zigzag pattern is formed by continously shifting jute 12 laterally back and forth as it travels longitudinally under needle bar 14. The jute is shifted laterally by a reciprocating drive mechanism which includes an elongated step-over bar 24 extending over the jute. The step-over bar is disposed in the plane parallel to and closely spaced apart downstream of needle bar 14. A drive arm 26 connected to one end of step-over bar 24 is driven back and forth laterally by suitable drive means (not shown) to reciprocate stepover bar 24.

An elongated pin roll 28 carried below step-over bar 24 is held tightly in contact with the top surface of the traveling jute backing sheet 12. The pin roll reciprocatcs laterally with the step-over bar to shift the jute back and forth during its travel under needle bar 14 so the tufting is applied in an appropriate zigzag pattern.

Selvedge strips 30 are provided along the marginal edges of the jute.

The tufting is maintained in its centered position on the jute by a centering and indicating system which includes a pair of edge sensors 32 for continuously sensing the position of opposite longitudinal edges 31 of jute backing sheet 12. As shown best in FIG. 2, each sensor 32 includes a vertically extending, pendulously supported elongated sensing arm 34 biased into contact with a respective edge 31 of the jute. Preferably, each sensing'arm is held in contact with the jute as close to the vertical plane of the needles 18 as possible, because the position of the jute along the plane where the tufting is applied is the parameter to be sensed and controlled. Each sensing arm 34 is carried on the end of an elongated shaft 36 extending outwardly from the front end of a rotatable cylindrical housing 38 mounted above a respective edge 31 of the jute. Each shaft 36 rotates about a horizontal axis extending in the same general direction as the corresponding edge 31 spaced below it. A corresponding drum 40 inside each housing 38 is engaged with shaft 36, and a spring 42 is wound on the drum to apply a constant bias to the bottom of the sensing arm to hold it in continuous contact with edge 31 of the jute. Rotation of shaft 36 in response to movement of sensing arm 34 moves a wiper arm 43 (represented schematically in FIG. 3) of a potentiometer (represented schematically at 44 in FIGS. 2 and 3) located in and fixed to housing 38. The resistance element of potentiometer 44 and wiper arm 43 are connected to anelectrical connector (represented schematically at 45) in housing 38.

Each sensor 32 is supported by a separate rotating rod 46 extending into the rear of housing 38. Each rod 46 is journaled in a corresponding bearing 48 and is driven by step-over bar 24 (in a manner described in detail below). During operation of the tufting machine, lateral movement of the jute moves the sensing arm which rotates shaft 36. The shaft drives wiper arm 43, and rod 46 drives the resistance element of the potentiometer independently of the wiper arm. Rod 46 is fixed to housing 38 and causes the housing and the potentiometer resistance element 44 to rotate as a unit in response to the lateral movement of the step-over bar. The housing does not rotate when the jute stepover bar is not used, but the sensing arms continue to follow movement of the jute.

The end of each rod 46 is connected to a separate upright lever arm 50, and both lever arms are intercon nected by a pair of horizontally disposed, collinear cross-bars 52 extending laterally above jute 12. Crossbars 52 are mutually connected to an upright link arm 54 located above the center of the jute. The bottom of link arm 54 is connected to a reciprocating drive linkage operated by the reciprocating motion of step-over bar 24. The linkage includes a horizontally disposed elongated drive arm 56 fixed at one end to the stepover bar and having its opposite end connected to the bottom of an upright lever arm 58. An elongated rotation arm 60 journaled in a bearing 62 connects the top of lever arm 58 with the bottom of link arm 54.

In use, the reciprocating travel of step-over bar 24 causes the linkage to reciprocate cross-bars 52 which, in turn, rotate rod 46 and cause sensor housing 38 and its corresponding potentiometer element 44 to follow the laterally shifting motion of the step-over bar. Springs 42 constantly bias sensing arms 34 against longitudinal edges 31 of the jute so the edges of the jute can independently drive the wiper arms 43 of potentiometers 44. As the jute is shifted back and forth during tufting operations, wiper arms 43 and potentiometer elements 44 move back and forth, but there is no relative movement between each wiper arm 43 and its corresponding resistance element as long as the jute remains centered. In essence, the movement of potentiometer elements 44 in response to the step-over bar movement marks the desired on-center position of the jute. The movement of wiper arms 43 in response to movement of sensing arms 34 marks the actual position of the jute. Each potentiometer produces an output voltage of a given magnitude when the jute is oncenter. If the jute strays off-center, the voltage signals vary in accordance with the size of the deviation, and its direction, right or left, from a given reference point.

Electrical leads and 72 from the wiper arms of sensors 32 are fed to a meter relay 68 which indicates the deviation of the jute from its known centered position. The operation of meter relay 68 is understood best by referring to FIGS. 3 and 4. FIG. 3 shows an electrical schematic diagram of the meter relay which preferablycomprises a Compack IV Solid State Controller manufactured by API Instruments Company, Chesterland, Ohio. The meter relay is operated by a DC input voltage produced by connecting potentiometer .44 of sensors 32 into a bridge arrangement illustrated in FIGv 3; Wiper arms 43 are coupled with corresponding lead wires and 72 which provide the voltage input to meter relay 68.

In use, the meter relay is calibrated by initially centeringjute backing sheet 12 on the tufting machine and then adjusting sensing arms 34 and their associated linkage so that the voltage signal carried by lead wire 70 is offset by the voltage signal in lead wire 72, thereby resulting in a zero input voltage to the meter relay. Thereafter, as the jute travels through the tufting machine, lateral movement of the jute will cause wiper arms 43 to move back and forth to indicate the actual position of the edges of the jute. The step-over bar will rotate rods 46 to move potentiometer resistance elements 44 back and forth indicating the true on-center position of the jute. As long as the jute backing sheet remains centered on the tufting machine, the meter relay will cause the voltage of one potentiometer to be offset by the voltage of the other, and will produce a zero voltage which is fed to a meter 74. The zero voltage will produce a neutral scale reading on meter 74, indicating that the jute is on-center.

If the jute backing sheet goes off-center, a difference in potentiometer voltages is developed by the bridge circuit. This voltage difference is fed to a voltage divider and DC amplifier circuit (represented schematically at 76) which produces an output voltage at 78 proportional to the magnitude of the voltage difference developed across the bridge. The polarity of voltage signal 78 will depend upon which edge of the jute is moving away from an imaginary central longitudinal axis through the tufting machine. Voltage signal 78 is fed to meter 74 to drive an indicator needle 80 (see FIG. 4) which provides a continuous scale reading of the size of the deviation (in inches) from the on-center position, and the direction of the deviation from the imaginary central axis.

By increasing or decreasing voltage V the gain across the bridge circuit can be changed so the meter scale factor can be adjusted to read the desired number of inches in deviation for a given voltage input.

Meter relay 68 also includes a potentiometer 82 having a high set point wiper and related circuitry (represented schematically at 84) and a low set point wiper and related circuitry (represented schematically at 86). The position of the high set point wiper is selectively adjusted by a knob 88 on the control panel of the meter relay to produce an output voltage signal at 90 proportional to the desired maximum allowable deviation of one longitudinal edge of the jute from the on-center position. Similarly, the position of the low set point wiper is selectively adjusted by a knob 92 to produce an output voltage signal at 94 proportional to the desired maximum allowable deviation of the other longitudinal edge of the jute from the on-center position. The posi tion of the high set point wiper is indicated by a needle 96 on meter 74, and a needle 98 on the meter indicates the position of the low set point wiper.

Voltage signal 78 is fed to both a high set point comparator 100 and a low set point comparator 102. Comparator 100 compares voltage 78 with wiper voltage 90 and produces an output voltage signal at 104 when the comparison of the two signals indicates that one edge or the center of the jute has exceeded its allowable deviation from the center of the machine. Similarly, comparator 102 compares voltage 78 with low set point wiper voltage 94 and produces an output voltage signal at 106 when the comparison of the two signals indicates that the other edge of the jute has exceeded its allowable deviation. Signal 104 energizes a relay 108 which produces a right error signal 109 for activating a suitable alarm l10 to indicate that the right edge or the center of the jute has exceeded its allowable deviation. Signal 106 energizes a relay 112 which produces a left error signal 113 for activating a second alarm 114 indicating that the left edge or center of the jute has exceeded its allowable deviation. Preferably, alarms and 114 comprise warning lights (shown in FIG. 4) mounted on the meter relay control panel, although the alarms can take other forms such as audible warning devices, or the like.

FIG. 5 shows a brief electrical schematic diagram of a controller 115 for automatically moving the jute 12 back toward its on-center position in response to either a right error signal 109 or a left error signal 113. The controller produces an output which drives a servo motor 118 coupled to the jute storage roll 13 for moving the storage roll laterally to automatically keep the jute on-center. When a right error signal 109 is present, the signal closes the normally open contacts of a pair of relays 120 and 122 for completing a circuit which ultimately generates a right correction signal. Similarly, when a left error signal is generated, the signal closes the contacts ofa pair of relays 124 and 126 to complete a circuit for generating a left correction signal. The right or left error signal 109 or 113 initially is fed to a delay timer 128 which includes a normally closed contact 130 that opens when a signal 152 is received from a correction timer 134 at the end of the correction timers correction cycle. The contact 130 remains open for the duration of one delay cycle of the delay timer to avoid receiving further error signals until the control cycle is completed. The control cycle is comprised of first the correction cycle and then the delay cycle.

After the delay timer receives either error signal 109 or 113, it generates an output signal 132 which triggers the correction timer 134. The correction timer includes a first normally open contact 136 which closes when the correction timer is triggered to produce a control signal 138 for driving the servo motor 118. If the right error signal 109 triggers the control cycle, then the control signal 138 drives the servo motor to produce a right correction. Conversely, if the left error signal 113 triggers the control cycle, then the control signal 138 drives the servo motor to produce a left correction.

The servo motor 118 preferably is a three-phase motor driven by a reversing motor starter contacter. As shown in FIG. 6, the output shaft of the motor rotates an elongated jack screw 140 about an axis through a pair of spaced apart bearings 142. A fork 144 engaged with the jack screw either moves to the left or to the right under rotation of the jack screw when the motor rotates in response to a left correction or a right correction, respectively. The fork extends between a pair of spaced apart collars 146 affixed to the shaft 148 about which the jute supply roll 13 rotates. Longitudinal movement of the fork 144 in response to rotation of the jack screw 140 moves the shaft 148 and the jute supply roll 13 laterally in either the left or the right direction depending upon which correction signal is fed to the servo motor.

The time period of the correction timer 134 controls the distance through which the supply roll 13 is shifted during each control cycle. The correction timer includes means for selectively adjusting the length of time the contact 136 will remain closed during each control cycle which, in turn, provides an adjustable control over the distance through which the supply roll is moved during the control cycle. Thus, once the time period of the correction time is set, the servo motor will drive the supply roll 13 either to the right or the left for a fixed distance during each control cycle independently of the magnitude of the right or left error signals 109, 113.

After the correction timer period elapses, contact 136 opens and a second contact 150 in the correction timer momentarily closes and opens to produce the signal 152 for triggering the delay timer. The contacts in the relays 120, 122 or 124, 126 open at the end of the correction time period. The delay timer produces a delay time between the end of one corrective effort and the beginning of the next corrective effort. The delay timer includes means for selectively adjusting the length of the delay time independently of the adjustment for the period of the correction timer. After the preset delay time elapses, contact 130 closes and another control cycle can begin when either a left or right error signal is generated.

Thus the controller, in effect, periodically samples the existing right or left error signal and then produces an appropriate corrective effort to move the jute back toward its on-center position. The delay time between corrective efforts compensates for the fact that the plane in which the sensors 34 are located is spaced a substantial distance (about 15 seconds of machine travel time) from the plane of the supply roll 13 where the corrective effort takes place. The system allows each correction to be made by the servo motor, and then provides a suitable delay time for allowing the correction to take effect where the sensors are located, after which the existing error is again sampled to determine whethcr further correction is necessary.

Thus, the present invention provides a system for continuously sensing and controlling the position of work continuously fed through a machine along a known centered position. Sensing arms 34 provide means for constantly sensing the location of the oppo site edges of the work, and the deviation of the work from its on-center position is determined independently of any lateral movement of the work through the machine or variations in the width of the work. Moreover, the output generated by the sensing arms is used to drive a closed loop system for automatically adjusting the lateral position of the roll on which the jute is wound to keep the jute on-center. Thus, centering is accomplished even though the jute is being constantly shifted back and forth by the machine, and even though the width of the jute varies several inches from one plane to another in the roll. Thus, the difficult task of visually monitoring the on-center position of the jute is avoided.

I claim:

1. In a machine for operating on work having a desired centered position in the machine, the work being fed along a longitudinal path and being in contact with positioning means for adjusting the lateral position of the work relative to the desired centered position, the work being defined by spaced apart first and second longitudinal edges, apparatus for controlling the centering of the work in the machine independently of the width of the work or any lateral movement of the desired centered position of the work as it travels through the machine, the apparatus comprising first and second sensing means to sense the corresponding positions of the first and second longitudinal edges of the work; means coupled with the first sensing means to produce a first output representing the instantaneous position of the first longitudinal edge; means coupled with the second sensing means to produce a second output repre' senting the instantaneous position of the second longitudinal edge; means responsive to the first and second outputs for producing an error signal indicating a deviation of the work from its centered position; and closed loop feedback means for controlling the centered position of the work, the closed loop feedback means including means responsive to the error signal indicating that the first edge of the work deviates a predetermined distance from the desired centered position for producing a first correction signal, means responsive to the error signal indicating that the second edge of the work deviates a predetermined distance from the desired centered position for producing a second correction signal, and means responsive to either the first or second correction signal for adjusting the work positioning means to automatically move the work back toward its desired centered position, the first or second correction signal being periodically produced by a corrective timer responsive to the presence of an existing error signal to move the work positioning means for a selected time period in a direction which moves the work back toward its centered position.

2. Apparatus according to claim 1 in which the plane where the sensing means are located is spaced longitudinally from the plane where the work positioning means is located, and in which the closed loop feedback means includes means for controlling the lateral adjusting means by periodically sampling the existing error signal and producing a corresponding adjustment of the work positioning means.

3. Apparatus according to claim 2 in which the feedback control means includes means for producing a time delay after each adjustment of the work positioning means.

4. Apparatus according to claim 3 including means for adjusting the length of the time delay.

5. Apparatus according to claim 1 in which the time period of the corrective timer is adjustable.

6. In a machine for operating on work fed through the machine along a longitudinal path, the work having a width defined by a pair of spaced apart first and second longitudinal edges, and in which the machine includes lateral shifting means for moving the work laterally back and forth relative to an imaginary longitudinal axis through the machine as the work travels along said longitudinal path, the work having a desired on-center position which moves laterally back and forth relative to said imaginary axis in response to lateral shifting of the work, apparatus for maintaining the work on its desired on-center position as the work shifts laterally and moves longitudinally through the machine, the apparatus comprising means for continuously sensing movement of the actual position of each longitudinal edge of the work relative to said imaginary axis, independently of variations in the width of the work, as the edges are shifted laterally back and forth by the lateral shifting means,

means responsive to movement of the lateral shifting means for sensing lateral movement of the desired on-center position of the work relative to said imaginary axis as the work is shifted laterally back and forth,

means responsive to the sensed actual position of each longitudinal edge for comparing the actual position of the work with the sensed desired oncenter position of the work to produce an error signal representing the lateral deviation of the work from its desired on-center position, and

feedback control means responsive to the error signal and operative independently of movement by the lateral shifting means for adjusting the lateral position of the work to move the work toward the desired on-center position.

7. Apparatus according to claim 6 including work positioning means spaced longitudinally from the lateral shifting means and movable independently of the lateral shifting means for adjusting the lateral position of the work relative to said imaginary axis, and means responsive to the error signal for adjusting the lateral position of the work positioning means to automatically move the work back toward its on-center position. 7

8. Apparatus according to claim 7 in which the plane where the sensing means are located is spaced longitudinally from the plane where the work positioning means is located, and in which the feedback means includes means for controlling the work positioning means to periodically sample the existing error signal and produce a corresponding adjustment of the work positioning means.

9. Apparatus according to claim 8 in which the feed back control means includes means for producing a time delay after each adjustment of the work positioning means.

10. Apparatus according to claim 9 including means for adjusting the length of the time delay.

11. Apparatus according to claim 9 in which the feedback control means includes means responsive to the error signal indicating that one longitudinal edge of the work deviates a predetermined distance from the desired on-center position for producing a first correction signal, means responsive to the error signal indicating that the other longitudinal edge of the work deviates a predetermined distance from the desired oncenter position to produce a second correction signal, means responsive to either the first or second correction signal for adjusting the lateral position of the work positioning means, and a corrective timer responsive to the presence of an existing error signal for periodically producing either the first or second correction signal to move the work positioning means for a selected time period in a direction which moves the sheet laterally toward its on-center position.

12. Apparatus according to claim 11 including means for adjusting the time period of the corrective timer.

13. Apparatus for centering a continuous work sheet fed along a longitudinal path through a machine for working on the sheet and in which the sheet is continuously being shifted laterally back and forth as it travels longitudinally through the machine, the sheet having a desired on-center position with respect to the machine and a width defined by laterally spaced apart first and second longitudinal edges, the apparatus comprising first and second sensing arms continuously held in contact with the first and second longitudinal edges, respectively, of the sheet and being movable to follow the actual lateral movement of the first and second edges as the sheet is being shifted laterally back and forth during its travel through the machine, means responsive to movement of the first sensing arm for producing a first input representative of the actual position of the first edge of the sheet,

means responsive to movement of the second sensing arm for producing a second input representative of the actual position of the second edge of the sheet,

means for sensing the desired on-center position of the sheet as the sheet is being shifted laterally back and forth during its travel through the machine,

means responsive to the first and second inputs for comparing the actual position of the work sheet with the sensed desired on-center position of the sheet to produce an error signal representing the lateral deviation of the sheet from its desired on center position, and

feedback control means responsive to the error signal for adjusting the lateral position of the sheet to move the sheet toward the desired on-center position.

14. Apparatus according to claim 13 including laterally movable work positioning means in contact with the sheet for adjusting the lateral position of the sheet to move the sheet toward the desired oncenter position, and means responsive to the error signal for adjusting the lateral position of the work positioning means to automatically move the sheet laterally toward its on-center position.

15. Apparatus according to claim 14 in which the plane where the first and second sensing arms are located is spaced longitudinally from the plane where the work positioning means is located, and in which the feedback control means includes means for periodically sampling the existing error signal to produce a corresponding adjustment of the work positioning means.

16. Apparatus according to claim 15 in which the feedback control means includes means for producing a time delay after each adjustment of the work positioning means.

17. Apparatus according to claim 16 in which the feedback control means includes means responsive to the error signal indicating that the first edge of the work deviates a predetermined distance from the desired on-center position for producing a first correction signal, means responsive to the error signal indicating that the second edge of the work deviates a predetermined distance from the desired on-center position to produce a second correction signal, means responsive to the first and second correction signals for producing the error signal for adjusting the lateral position of the work positioning means, and a corrective timer responsive to the presence of an existing error signal for periodically producing either the first or second correction signal to move the work positioning means for a selected time period in a direction which moves the sheet laterally toward its on-center position.

18. Apparatus according to claim 17 in which the length of the time delay period is selectively adjustable independently of the time period of the corrective timer.

19. Apparatus according to claim 13 including first and second electrical elements movable in response to the first and second sensing arms, and third and fourth electrical elements movable in response to lateral shifting of the sheet to indicate the desired on-center posi tion of the sheet, the relative movement of the first and third electrical elements cooperating to produce a first electrical output, the relative movement of the second and fourth electrical elements cooperating to produce a second electrical output, the first and second electrical outputs being compared to produce an electrical output signal representing the lateral deviation of the sheet from its desired on-center position.

20. Apparatus according to claim 19 in which the lateral shifting means includes a laterally extending, elongated step-over bar having means on it for engaging the continuous sheet, drive means engaged with the stepover bar for shifting the bar to move the work sheet laterally back and forth as it travels longitudinally through the machine, the third and fourth electrical elements being connected to the step-over bar so the third and fourth electrical elements follow the lateral shifting movement of the bar, the first and second sensing arms being adapted to drive the first and second electrical elements, respectively, so they follow the lateral shifting positions of the longitudinal edges of the sheet.

21. Apparatus for sensing the centered position of a web of varying width traveling along a longitudinal path through a machine for working on the web, the web having a width defined by laterally spaced apart first and second longitudinal edges, the apparatus comprisa. a lateral shifting device engaged with the continuous web for shifting the web laterally back and forth as it travels longitudinally through the machine,

b. first and second sensing devices held in continuous contact with the first and second longitudinal edges and being movable to continuously follow lateral movement of the edges of the web as it travels longitudinally through the machine.

c. means responsive to movement of the first sensing device for continuously providing a first indication representing lateral movement of the first edge,

d. means responsive to movement of the second sensing device for continuously providing a second indication representing lateral movement of the second edge,

e. means responsive to movement of the lateral shifting device to sense lateral movement of the desired on-center position of the web, and

f. means for comparing the first and second indications with the sensed on-center position of the web to produce an output representing the lateral deviation of the web from its desired on-center position.

22. Apparatus according to claim 21 in which the means for sensing lateral movement of the on-center position of the web comprise means connected to the lateral shifting device for providing third and fourth indications each representing the lateral shifting movement of the desired on-center position of the web; an electrical bridge circuit in which the first, second, third, and fourth indications comprise respective electrical circuit elements balanced so that the first and second electrical elements provide a first electrical output and the third and fourth electrical elements provide a second electrical output; and means for comparing the first and second electrical outputs to produce said output representing the lateral deviation of the web from its desired on-center position.

23. Apparatus according to claim 21 including feedback control means responsive to the output representing said lateral deviation of the web for adjusting the lateral position of the web to move the web toward its desired on-center position.

24. Apparatus according to claim 23 including lateral position adjusting means engaged with the web and spaced longitudinally from said lateral shifting device, the position adjusting means being responsive to the output representing said lateral deviation to move the web toward its desired on-center position.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION 3,908,881 September 30, 1975 Patent No. Dated Gary D. McCann et 211. Inventor(s) It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

The term of this patent subsequent to April 23, 1991 has Been disclaimed.

Signed and Scaled this second Day of December1975 [SEAL] Arrest:

RUTH C. MASON C. MARSHALL BARN Arresting Officer Commissioner 1mm; and Trademlrks 

1. In a machine for operating on work having a desired centered position in the machine, the work being fed along a longitudinal path and being in contact with positioning means for adjusting the lateral position of the work relative to the desired centered position, the work being defined by spaced apart first and second longitudinal edges, apparatus for controlling the centering of the work in the machine independently of the width of the work or any lateral movement of the desired centered position of the work as it travels through the machine, the apparatus comprising first and second sensing means to sense the corresponding positions of the first and second longitudinal edges of the work; means coupled with the first sensing means to produce a first output representing the instantaneous position of the first longitudinal edge; means coupled with the second sensing means to produce a second output representing the instantaneous position of the second longitudinal edge; means responsive to the first and second outputs for producing an error signal indicating a deviation of the work from its centered position; and closed loop feedback means for controlling the centered position of the work, the closed loop feedback means including means responsive to the error signal indicating that the first edge of the work deviates a predetermined distance from the desired centered position for producing a first correction signal, means responsive to the error signal indicating that the second edge of the work deviates a predetermined distance from the desired centered position for producing a second correction signal, and means responsive to either the first or second correction signal for adjusting the work positioning means to automatically move the work back toward its desired centered position, the first or second correction signal being periodically produced by a corrective timer responsive to the presence of an existing error signal to move the work positioning means for a selected time period in a direction which moves the work back toward its centered position.
 2. Apparatus according to claim 1 in which the plane where the sensing means are located is spaced longitudinally from the plane where the work positioning means is located, and in which the closed loop feedback means includes means for controlling the lateral adjusting means by periodically sampling the existing error signal and producing a corresponding adjustment of the work positioning means.
 3. Apparatus according to claim 2 in which the feedback control means includes means for producing a time delay after each adjustment of the work positioning means.
 4. Apparatus according to claim 3 including means for adjusting the length of the time delay.
 5. Apparatus according to claim 1 in which the time period of the corrective timer is adjustable.
 6. In a machine for operating on work fed through the machine along a longitudinal path, the work having a width defined by a pair of spaced apart first and second longitudinal edges, and in which the machine inCludes lateral shifting means for moving the work laterally back and forth relative to an imaginary longitudinal axis through the machine as the work travels along said longitudinal path, the work having a desired on-center position which moves laterally back and forth relative to said imaginary axis in response to lateral shifting of the work, apparatus for maintaining the work on its desired on-center position as the work shifts laterally and moves longitudinally through the machine, the apparatus comprising means for continuously sensing movement of the actual position of each longitudinal edge of the work relative to said imaginary axis, independently of variations in the width of the work, as the edges are shifted laterally back and forth by the lateral shifting means, means responsive to movement of the lateral shifting means for sensing lateral movement of the desired on-center position of the work relative to said imaginary axis as the work is shifted laterally back and forth, means responsive to the sensed actual position of each longitudinal edge for comparing the actual position of the work with the sensed desired on-center position of the work to produce an error signal representing the lateral deviation of the work from its desired on-center position, and feedback control means responsive to the error signal and operative independently of movement by the lateral shifting means for adjusting the lateral position of the work to move the work toward the desired on-center position.
 7. Apparatus according to claim 6 including work positioning means spaced longitudinally from the lateral shifting means and movable independently of the lateral shifting means for adjusting the lateral position of the work relative to said imaginary axis, and means responsive to the error signal for adjusting the lateral position of the work positioning means to automatically move the work back toward its on-center position.
 8. Apparatus according to claim 7 in which the plane where the sensing means are located is spaced longitudinally from the plane where the work positioning means is located, and in which the feedback means includes means for controlling the work positioning means to periodically sample the existing error signal and produce a corresponding adjustment of the work positioning means.
 9. Apparatus according to claim 8 in which the feedback control means includes means for producing a time delay after each adjustment of the work positioning means.
 10. Apparatus according to claim 9 including means for adjusting the length of the time delay.
 11. Apparatus according to claim 9 in which the feedback control means includes means responsive to the error signal indicating that one longitudinal edge of the work deviates a predetermined distance from the desired on-center position for producing a first correction signal, means responsive to the error signal indicating that the other longitudinal edge of the work deviates a predetermined distance from the desired on-center position to produce a second correction signal, means responsive to either the first or second correction signal for adjusting the lateral position of the work positioning means, and a corrective timer responsive to the presence of an existing error signal for periodically producing either the first or second correction signal to move the work positioning means for a selected time period in a direction which moves the sheet laterally toward its on-center position.
 12. Apparatus according to claim 11 including means for adjusting the time period of the corrective timer.
 13. Apparatus for centering a continuous work sheet fed along a longitudinal path through a machine for working on the sheet and in which the sheet is continuously being shifted laterally back and forth as it travels longitudinally through the machine, the sheet having a desired on-center position with respect to the machine and a width defined by laterally spaced apart first and second longituDinal edges, the apparatus comprising first and second sensing arms continuously held in contact with the first and second longitudinal edges, respectively, of the sheet and being movable to follow the actual lateral movement of the first and second edges as the sheet is being shifted laterally back and forth during its travel through the machine, means responsive to movement of the first sensing arm for producing a first input representative of the actual position of the first edge of the sheet, means responsive to movement of the second sensing arm for producing a second input representative of the actual position of the second edge of the sheet, means for sensing the desired on-center position of the sheet as the sheet is being shifted laterally back and forth during its travel through the machine, means responsive to the first and second inputs for comparing the actual position of the work sheet with the sensed desired on-center position of the sheet to produce an error signal representing the lateral deviation of the sheet from its desired on-center position, and feedback control means responsive to the error signal for adjusting the lateral position of the sheet to move the sheet toward the desired on-center position.
 14. Apparatus according to claim 13 including laterally movable work positioning means in contact with the sheet for adjusting the lateral position of the sheet to move the sheet toward the desired on-center position, and means responsive to the error signal for adjusting the lateral position of the work positioning means to automatically move the sheet laterally toward its on-center position.
 15. Apparatus according to claim 14 in which the plane where the first and second sensing arms are located is spaced longitudinally from the plane where the work positioning means is located, and in which the feedback control means includes means for periodically sampling the existing error signal to produce a corresponding adjustment of the work positioning means.
 16. Apparatus according to claim 15 in which the feedback control means includes means for producing a time delay after each adjustment of the work positioning means.
 17. Apparatus according to claim 16 in which the feedback control means includes means responsive to the error signal indicating that the first edge of the work deviates a predetermined distance from the desired on-center position for producing a first correction signal, means responsive to the error signal indicating that the second edge of the work deviates a predetermined distance from the desired on-center position to produce a second correction signal, means responsive to the first and second correction signals for producing the error signal for adjusting the lateral position of the work positioning means, and a corrective timer responsive to the presence of an existing error signal for periodically producing either the first or second correction signal to move the work positioning means for a selected time period in a direction which moves the sheet laterally toward its on-center position.
 18. Apparatus according to claim 17 in which the length of the time delay period is selectively adjustable independently of the time period of the corrective timer.
 19. Apparatus according to claim 13 including first and second electrical elements movable in response to the first and second sensing arms, and third and fourth electrical elements movable in response to lateral shifting of the sheet to indicate the desired on-center position of the sheet, the relative movement of the first and third electrical elements cooperating to produce a first electrical output, the relative movement of the second and fourth electrical elements cooperating to produce a second electrical output, the first and second electrical outputs being compared to produce an electrical output signal representing the lateral deviation of the sheet from its desired on-center position.
 20. Apparatus acCording to claim 19 in which the lateral shifting means includes a laterally extending, elongated step-over bar having means on it for engaging the continuous sheet, drive means engaged with the step-over bar for shifting the bar to move the work sheet laterally back and forth as it travels longitudinally through the machine, the third and fourth electrical elements being connected to the step-over bar so the third and fourth electrical elements follow the lateral shifting movement of the bar, the first and second sensing arms being adapted to drive the first and second electrical elements, respectively, so they follow the lateral shifting positions of the longitudinal edges of the sheet.
 21. Apparatus for sensing the centered position of a web of varying width traveling along a longitudinal path through a machine for working on the web, the web having a width defined by laterally spaced apart first and second longitudinal edges, the apparatus comprising a. a lateral shifting device engaged with the continuous web for shifting the web laterally back and forth as it travels longitudinally through the machine, b. first and second sensing devices held in continuous contact with the first and second longitudinal edges and being movable to continuously follow lateral movement of the edges of the web as it travels longitudinally through the machine. c. means responsive to movement of the first sensing device for continuously providing a first indication representing lateral movement of the first edge, d. means responsive to movement of the second sensing device for continuously providing a second indication representing lateral movement of the second edge, e. means responsive to movement of the lateral shifting device to sense lateral movement of the desired on-center position of the web, and f. means for comparing the first and second indications with the sensed on-center position of the web to produce an output representing the lateral deviation of the web from its desired on-center position.
 22. Apparatus according to claim 21 in which the means for sensing lateral movement of the on-center position of the web comprise means connected to the lateral shifting device for providing third and fourth indications each representing the lateral shifting movement of the desired on-center position of the web; an electrical bridge circuit in which the first, second, third, and fourth indications comprise respective electrical circuit elements balanced so that the first and second electrical elements provide a first electrical output and the third and fourth electrical elements provide a second electrical output; and means for comparing the first and second electrical outputs to produce said output representing the lateral deviation of the web from its desired on-center position.
 23. Apparatus according to claim 21 including feedback control means responsive to the output representing said lateral deviation of the web for adjusting the lateral position of the web to move the web toward its desired on-center position.
 24. Apparatus according to claim 23 including lateral position adjusting means engaged with the web and spaced longitudinally from said lateral shifting device, the position adjusting means being responsive to the output representing said lateral deviation to move the web toward its desired on-center position. 